Printed Circuit Board (PCBA)

Light curing in electronics:

Light curing encapsulants, coatings, adhesives are increasingly widely used in the field of electrical and electronic components manufacturing. They are a right fit for the prevailing manufacturing requirements that are dictated by the present industry drivers, such as manufacturing yield improvement, miniaturization, environmental/health/safety demands, and energy conservation.

When it comes to a UV curing system for electronic applications, this type of system is mainly based on UV-curable acrylic and urethane chemistries, although UV-curable epoxy and silicone are also known. In simple terms, these UV-curable materials consist of oligomers, monomers, and a variety of agents/photo-initiators/modifier molecules. Normally, these elements can coexist; they don’t react with each other unless they are exposed to ultraviolet light of the correct intensity and wavelength. And when exposed to UV light, those elements undergo cleavage and generate “free radicals” (a type of highly energetic oxygen molecules), which trigger the formation of monomer chains. In most cases, such a light-curing process is instantaneous.

The general benefits and features of light-curing coatings and adhesives can be summarized as below:

  • Fast cure within a matter of seconds.
  • 100% solids and solvent-free.
  • Unlimited pot life.
  • Ambient temperature cure.
  • Available in various viscosities.
  • Excellent thermal and moisture resistance.
  • Relatively low energy cure.
  • Cured grades from hard to flexible.
  • Good adhesion to a vast range of substrates.
  • Low toxicity with little odor.
  • Will not bond skin.
  • Easily adapt to automated applications.

Next, let’s talk about the specific electronic applications that involve UV curing technology：

Actually, the use of UV curing technology has already been found in hundreds of applications in the electronic manufacturing industry. Those successful applications have repeatedly proven the economics and efficacy of using UV-curable adhesives and coatings. And the following just lists some typical areas:

  • Strain relief against shock and vibration of components.
  • Coil terminating.
  • Wire and parts tacking.
  • Structural bonding.
  • Tamper-proofing.
  • Conformal coating.
  • Encapsulation, underfill, glob topping.
  • Surface mount component attachment.

The effective wavelength for a UV curing system:

The majority of curable adhesives are cured with ultraviolet light. Historically, the first coatings and inks were dried with shortwave UV light within the 250 nm range; but short-wavelength (UV-C: 100~280 nm) light is hazardous for health; now UV-C light is primarily used for sterilization not curing. In the electronic manufacturing industry, the common UV light that is used to cure adhesives belongs to long-wavelength (UV-A: 315~400 nm) light. And UV-A is considered the safest of the three spectra of UV light (UV-A, UV-B, and UV-C).

The curing speeding:

Compared with minutes or even hours for conventional curing systems like heat curing and solvent evaporation drying, UV light curing offers more benefits, UV light curing is powerful, the curable adhesive can be cured within seconds; in addition, the synergistic use of both photo-catalysts in adhesive formulations and long-wavelength light can cure up to 50% faster than formulations that cure only by absorbed UV light.

The curing depth:

The light absorption of UV curable materials varies with wavelength. Generally, a short-wavelength UV light can be well absorbed by the very surface of materials. By contrast, because curable materials absorb a long-wavelength UV light less well so that the light can penetrate further. Therefore, in those applications such as structural sealing, coating, and bonding where the curing depths are required to reach several millimeters, a UV light source with a relatively long wavelength can help users achieve better results. Therefore, in the electronic manufacturing industry, long-wavelength UV light is restricted to shallow sealing, potting, bridge bonding, and tacking applications; furthermore, encapsulation and deep potting are also limited to the use of clear resins or thin coats of pigmented resins.

UV-curable materials:

By adding the visible light-sensitive photocatalysts into the formulations, the range of UV-curable materials that can be bonded, potted, or sealed increases substantially. In fact, any material that can be seen through can be a candidate for use in adhesive light curing. Currently, in the electronic industry, common materials that are used to transmit sufficient curing light include polyimide films, UV opaque plastics, translucent plastics, glasses, and crystals.